Robots and robotic devices are used today to perform tasks traditionally considered dangerous or otherwise inappropriate for humans, due to size or environmental considerations. For example, robots are often purposefully exposed to situations where the risk to a human being in a similar situation is too high. In one illustrative example, explosive ordnance disposal (“EOD”) robots are used to approach, inspect, and even remove or defuse explosives or objects that may contain explosives. Generally, a human operator of an EOD robot remains at a safe distance from the explosive (or possibly explosive) object and directs the EOD robot remotely as it performs its necessary tasks. Even though the EOD robots are often driven by remote control, incorporation of a physical tether between the robot and a base station near the operator is often favored. Tethered robots and other robotic platforms are being developed. For example, U.S. Pat. Nos. 6,263,989, 6,431296, and 6,668,951 each disclose Robotic Platforms, the disclosures of which are hereby incorporated by reference in their entireties.
The tether may include a fiber optic cable, to provide a reliable, high speed, non-electric connection for sending signals to and from on-board actuators and sensors, including cameras, thus allowing the operator to control the mobile robot and view the area in immediate proximity to the robot during use. Fiber optic cables are generally preferred over wireless transceivers, because signals sent over wireless systems can suffer from limited range and radio or environmental interference. Also, in certain situations (e.g., near an explosive device), radio frequency transmissions may not be allowed. These circumstances and restrictions can reduce the quality of communications and limit or end the mission. This is often the case indoors or underground, due to interference with surrounding building structure. Use of a tethered cable, however, does have its limitations, one of the most apparent being that cables trailed behind mobile robots can become snagged as the robot moves around corners or other obstacles. These snags, in addition to effecting the motion of the robot by creating a dragging force as the robot moves, also create high stress points on the cable, which can lead to intermittent communication or damage of the cable itself. Often, the cable is under a state of tension as the robot or vehicle moves ahead. If the robot turns in place this tension will often pull the cable directly into the moving parts of the mobility system, resulting in the cable becoming wound around an axle or tangled in the drive treads. Clearly, these problems increase as the robot moves within more complicated environments or structures.
To avoid these situations, cable handling systems have been developed that dispense cable behind a moving robot. Such handling systems generally utilize a reel of cable that rotates as the robot moves to pay out or draw in cable, in conjunction with some type of second device to detect and/or control cable tension. For example, some variations of these second devices detect strain in components that the cable passes through and compensate by paying out cable faster, thus relieving the strain. Still other devices include a sensor on a tensioning roller, remote from the main hub, that helps compensate for increases or decreases in speed of the robot, and distributes cable accordingly.
Many of these present spooler systems, however, are unable to compensate for abrupt changes in speed of the robot, or are unable to work effectively at high speed. Other cable handling systems are unable to accurately compensate for turns (especially turns described as neutral or “zero radius”) of the robot and either dispense or retract an insufficient or excessive length of cable. Other cable handling systems are bound to the input of a single variable to manage the cable and may pay out or draw in an improper amount of cable as long as that variable is satisfied, regardless of competing needs of the operating robot or surrounding environmental conditions.
There is, therefore, need for a spooler system that can reliably dispense and retrieve cable at various speeds, that is able to respond to abrupt changes in vehicle speed or cable tension, and that can accurately pay out and draw in cable, in an intelligent manner, during all types of maneuvers across a wide range of operational terrains.